v3.25.1
Risk/Return Detail Data - FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro
Apr. 29, 2025
USD ($)
Risk/Return:  
Registrant Name Fidelity Salem Street Trust
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond Index Fund  
Risk/Return:  
Risk/Return [Heading] Fund Summary Fund: Fidelity® SAI Intermediate Treasury Bond Index Fund
Objective [Heading] Investment Objective
Objective, Primary [Text Block] Fidelity® SAI Intermediate Treasury Bond Index Fund seeks a high level of current income.
Expense [Heading] Fee Table
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Text] Shareholder fees
(fees paid directly from your investment) none
Operating Expenses Caption [Text] Annual Operating Expenses
Fee Waiver or Reimbursement over Assets, Date of Termination Jun. 30, 2026
Portfolio Turnover [Heading] Portfolio Turnover
Portfolio Turnover [Text Block] The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund's performance. For the period from September 20, 2024 to February 28, 2025, the fund's portfolio turnover rate was 20 % of the average value of its portfolio.
Portfolio Turnover, Rate 20.00%
Other Expenses, New Fund, Based on Estimates [Text] Based on estimated amounts for the current fiscal year.
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:
Strategy [Heading] Principal Investment Strategies
Strategy Narrative [Text Block] Normally investing at least 80% of assets in securities included in the Bloomberg U.S. 5-10 Year Treasury Bond Index. The index is a market value-weighted index of investment-grade fixed-rate public obligations of the U.S. Treasury with maturities between five and ten years. Effective December 11, 2025, derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Normally maintaining a dollar-weighted average maturity that generally is expected to be between five and ten years, consistent with that of the index. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg U.S. 5-10 Year Treasury Bond Index using a smaller number of securities.
Risk [Heading] Principal Investment Risks
Bar Chart and Performance Table [Heading] Performance
Performance Narrative [Text Block] Performance history will be available for the fund after the fund has been in operation for one calendar year.
Performance One Year or Less [Text] Performance history will be available for the fund after the fund has been in operation for one calendar year.
FidelitySAIIntermediateTreasuryBondIndexFundFidelitySAIShort-TermTreasuryBondIndexFundPro | Fidelity SAI Intermediate Treasury Bond Index Fund | Fidelity SAI Intermediate Treasury Bond Index Fund  
Risk/Return:  
Management fee 0.03%
Distribution and/or Service (12b-1) fees none
Other expenses 0.02% [1]
Total annual operating expenses 0.05%
Fee waiver and/or expense reimbursement 0.02% [2]
Total annual operating expenses after fee waiver and/or expense reimbursement 0.03%
1 year $ 3
3 years $ 13
[1]
A Based on estimated amounts for the current fiscal year.
[2]
B Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.03% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through June 30, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.